Shaft for use in golf clubs and other shaft-based instruments and method of making the same

ABSTRACT

A shaft for use in a golf-club or other shaft-based instrument, including a base member and a metal layer, and a method of making the same.

BACKGROUND OF THE INVENTIONS

1. Field of the Inventions

The present inventions relate generally to shaft-based instruments and,more particularly, to shafts for use in golf clubs and other shaft-basedinstruments.

2. Description of the Related Art

Over the years, there have been a variety of attempts to improveshaft-based instruments such as golf clubs, ski poles and hockey sticks.With respect to golf clubs, many substitutes have been introduced forthe hard wood shafts originally used in golf club drivers and irons.Early substitute materials included stainless steel and aluminum. Morerecently, carbon fiber reinforced resin shafts have become popular. Suchshafts are typically hollow and consist of a shaft wall formed around atapered mandrel. The use of fiber reinforced resin has allowed golf clubmanufacturers to produce shafts having varying degrees of strength,flexibility and torsional stiffness. Carbon fiber reinforced resinshafts have also become popular in other shaft-based instruments. Assuch, manufacturers are able to produce shafts which suit the needs of awide variety of applications.

Nevertheless, manufactures of shaft-based instruments are faced with avariety of design issues that have proven difficult to overcome usingconventional fiber reinforced resin technologies. One issue associatedwith shaft design is related to the torsional and longitudinal stiffnessof the shafts and, in the golf club shaft context, the attempts ofdesigners to increase torsional stiffness (especially near the clubhead) in order to improve shot accuracy and increase longitudinalstiffness in order to cope with the ever increasing swing velocities ofgolfers. Another issue associated with shaft design is the location ofthe shaft flex point. More specifically, the inability of shaftdesigners to precisely predict the location of the flex point whendesigning a shaft without using excessive amounts of composite material,which can lead to weight and thickness issues, can be problematic.Breakage prevention is another important design issue. With respect togolf club shafts, for example, breakage often occurs within the regionof the main body section that is adjacent to the club head.

SUMMARY OF THE INVENTIONS

The general object of the present inventions is to provide shafts thateliminate, for practical purposes, the aforementioned problems. Inparticular, one object of the present inventions is to provide golf clubshafts and other shafts that have greater torsional and longitudinalstiffness than conventional fiber reinforced resin shafts. Anotherobject of the present inventions is to provide golf club shafts andother shafts which facilitate precise location of the flex point. Stillanother object of the present inventions is to provide golf club shaftsand other shaft that resist breakage.

In order to accomplish these and other objectives, a shaft in accordancewith the present invention includes a plurality of fiber reinforcedresin layers and a metal layer. The metal layer may, for example, beformed from a lightweight, high modulus of elasticity and tensilestrength material such as titanium. Such a shaft provides a number ofadvantages over conventional shafts. For example, the metal layeraugments the shafts torsional and longitudinal stiffness. Shaftdesigners can also adjust the location of the flex point by simplyadjusting the length of the metal layer. The metal layer will alsoprevent breakage. In golf club shafts, for example, the metal layer mayextend along the tip section from a point within the club head hosel toa point outside the hosel. This arrangement strengthens the area of thetip section adjacent to the club head that is a frequent area ofbreakage in conventional golf club shafts and also provides torsionalrigidity.

The above described and many other features and attendant advantages ofthe present inventions will become apparent as the inventions becomebetter understood by reference to the following detailed descriptionwhen considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Detailed description of preferred embodiments of the inventions will bemade with reference to the accompanying drawings.

FIG. 1 is a side view of a golf club in accordance with a preferredembodiment of a present invention.

FIG. 2 is a section view taken along line 2-2 in FIG. 1.

FIG. 3 is a partial, exploded view of the portion of the golf club shaftillustrated in FIG. 2.

FIG. 4 is a cutaway view of a portion of the golf club shaft illustratedin FIG. 1 with various layers of the shaft cutaway by different amountsto expose the layers.

FIG. 5 a is a section view of the tip region of the golf clubillustrated in FIG. 1.

FIG. 5 b is a plan view showing the relative sizes of the metal layerand outer layer in the golf club illustrated in FIG. 5 a.

FIG. 5 c is a section view of the tip region of a golf club inaccordance with a preferred embodiment of a present invention.

FIG. 5 d is a section view of the tip region of a golf club inaccordance with a preferred embodiment of a present invention.

FIG. 6 is a cutaway, partial section view of the golf club shaft inaccordance with a preferred embodiment of the present invention.

FIG. 7 is perspective view of a pair of metal layer members inaccordance with a preferred embodiment of a present invention.

FIG. 8 is a plan view of a metal layer blank in accordance with apreferred embodiment of a present invention.

FIG. 9 is a perspective view of the metal layer formed by the metallayer blank illustrated in FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is a detailed description of the best presently knownmodes of carrying out the inventions. This description is not to betaken in a limiting sense, but is made merely for the purpose ofillustrating the general principles of the inventions. The scope of theinventions is defined by the appended claims. Additionally, although thepresent inventions are described herein in the golf club shaft contextbecause the inventions are particularly well suited to golf club shafts,the inventions are not so limited. The inventor herein has determinedthat present inventions have application in other shaft-based devicessuch as, for example, ski poles and hockey sticks.

As illustrated for example in FIG. 1, a golf club shaft 10 in accordancewith a preferred embodiment of a present invention includes a hollowshaft 12, a grip 14, and a club head 16. The exemplary shaft 12 isdivided into three sections—the grip section 18 which is covered by thegrip 14, the tip section 20 which supports the club head 16, and themain body section 22 which extends from the distal end of the gripsection to the proximal end of the tip section. The tip section/mainbody section intersection is identified by reference numeral 23. In theillustrated embodiments, the grip section 18 is substantiallycylindrical, the tip section 20 is substantially cylindrical, and themain body section 22 has a frusto-conical shape with a substantiallyconstant taper. The exemplary shaft 12 also includes a butt (or“proximal”) end 24 and a tip (or “distal”) end 26. The presentinventions are not, however, limited to such a configuration. Other gripsection, tip section and main body section configurations and shapes,such as those disclosed in commonly assigned U.S. Pat. Nos. 5,944,618and 5,957,783, both of which are incorporated herein by reference, mayalso be employed.

It should be noted that the dimensions of the shafts illustrated in thedrawings are exaggerated and often not to scale. Commercial embodimentsof golf club shafts in accordance with the present inventions may rangefrom about 33 inches to about 46 inches in overall length. With respectto the tip section 20, the length may range from about 3 inches to about8 inches and the outer diameter (OD) may range from about 0.370 inch toabout 0.500 inch for irons and from about 0.335 inch to about 0.500 inchfor woods. The typical club head hosel, i.e. the portion of the clubhead that receives the shaft, is about 1 inch. Thus, the tip section 20will extend proximally beyond the hosel in the manner illustrated inFIGS. 1 and 5 a. The length of the grip section 18 may range from about6 inches to about 10 inches. The exemplary grip section may be eithersubstantially cylindrical (as shown) with an OD of about 0.58 inch toabout 0.62 inch or tapered from an OD of about 0.81 inch to about 1.0inch at the butt to an OD of about 0.55 inch to about 0.70 inch at thegrip section/main body section intersection. The wall thickness ispreferably between about 0.024 inch and about 0.059 inch (between about0.6 mm and about 1.5 mm).

The exemplary shaft 12 consists of two primary components—a polymer basemember 28 and a metal layer 30. Referring to FIGS. 2-4, the exemplarybase member 28 is a fiber reinforced resin base member that may beformed in conventional fashion by wrapping multiple layers (typically10-20 layers total) of a fiber reinforced resin composite over a mandreluntil the desired wall thickness is obtained. The layers are preferablyarranged in groups that each include a plurality of fiber reinforcedresin layers. In the illustrated embodiment, layer groups 32, 34 and 36are oriented at different angles with respect to the longitudinal axisof the shaft 12. The fibers within the respective layers of each groupare parallel to one another. More specifically, the fibers 32 a and 34 ain the layers within groups 32 and 34 are angled from 30-90 degrees withrespect to the longitudinal axis of the shaft, while the fibers 36 a inlayer group 36 are parallel to the longitudinal axis. Other layer andlayer group combinations may also be employed in embodiments of thepresent invention. For example, layer groups 32 and 34 may be combined(a total of 5-10 layers, for example) and the individual layers arrangedsuch that the fibers in successive layers are oriented at differentangles with respect to the longitudinal axis.

The exemplary base member 28 may be manufactured using any of thematerials typically used to produce composite resin/fiber golf clubshafts. Suitable resins include, for example, thermosetting resins orpolymers such as polyesters, epoxies, phenolics, melamines, silicones,polimides, polyurethanes and thermoplastics. Suitable fibers include,for example, carbon-based fibers such as graphite, glass fibers, aramidfibers, and extended chain polyethylene fibers. After the successivelayers of fiber reinforced resin are wrapped around the mandrel, theshaft is cured in an oven. Curing times and temperatures depend on thepolymer used in the composite and are well known to those of skill inthe art.

The metal layer 30 in the exemplary embodiments is preferably formedfrom a metal having relatively high tensile strength (about 200-350 Mpa)and a relatively high modulus of elasticity (about 70-200 GPa).Commercially pure titanium, 7000 series aluminum, and low alloy steelare suitable metals. Aluminum alloys, such as scandium-aluminum alloys,that have the desired tensile strength and modulus of elasticitycharacteristics may also be used. The thickness of the metal layer 30will range from about 0.001 inch to about 0.006 inch when formed fromthese materials. Although not so limited, the metal layer willpreferably be positioned such that it extends along the shaft from apoint on the shaft within the club head hosel to a point on the shaftoutside the club head hosel. This is because the area adjacent to theclub head 16 is the area which is most effected by torsional forces andis also the area where conventional shafts are most likely to break. Asillustrated in FIGS. 1 and 5 a, the metal layer 30 in the exemplaryembodiment is aligned with tip end 26 and extends along the tip section20 to a point distal of the main body section 22.

The length of the metal layer 30 will depend upon the dimensions of theoverall shaft 12 and the intended shaft characteristics, such asstiffness and flex point location. Suitable lengths for golf club shaftsrange from about 5 inches to about 30 inches. However, there may be someinstances where the metal layer 30 would extend over the entire lengthof the shaft. There may also be some instances where the metal layer 30would extend over only a portion of the tip section 20 that will not bewithin the club head hosel when the golf club is assembled (FIG. 5 c),or would extend over only some or all of the main body section 22 (FIG.5 d), or would extend over only some or all of the tip section and someor all of the main body section (FIG. 6), depending on the intendedresults. With respect to shafts for other shaft-base instruments, themetal layer may extend over the entire length of the base member, orover only a portion thereof, depending on the intended application.

The metal layer 30 is wrapped around the fiber reinforced resincomposite base member 28 through the use of a rolling process duringmanufacturing. The rolling process may be performed by hand or with arolling table. The metal sheet (or sheets) that make up the metal layer30 should preferably be sized such that the metal wraps exactly a wholenumber multiple of times around the base member 28, e.g. exactly onetime or exactly two times, but not 2½ times, in order to prevent theformation of spines.

Preferably, there will be a bonding layer 38 that secures the basemember 28 and metal layer 30 to one another in the manner illustratedfor example in FIGS. 3 and 4. The bonding layer 38, which hasapproximately the same measurements as the metal layer 30, can be formedfrom any suitable material. Suitable bonding layers include, but are notlimited to, high resin content scrim cloth (about 40% resin content byweight or higher), a sheet of epoxy, spray on epoxy, tacking film, and alayer of fiber reinforced resin that is pre-impregnated with epoxy(about 40% resin content or higher). The bonding layer 38 should besecured to the metal layer 30 prior to wrapping the metal layer 30around the base member 28. The bond between the metal layer 30 and thebonding layer 38 may be improved by roughening the surface of the metallayer that is in contact with the bonding layer prior to adding thebonding layer. This may be accomplished by, for example, chemicaletching, sand blasting, or brushing the surface of the metal sheet (orsheets) used to form the metal layer 30.

The metal layer 30 may have enough metal memory to cause it to unwind abit after the rolling process. Thus, although not required, theexemplary shaft 12 also includes an outer layer 40 that is used to holddown the metal layer 30. Suitable outer layers include high resincontent scrim cloth (about 40% resin content by weight or higher) andfiber reinforced resin that is pre-impregnated with epoxy (about 40%resin content or higher). The scrim cloth is advantageous in that themetal layer 30 will be visible through the scrim cloth. As shown in FIG.5 b, the outer layer 40 extends at least slightly beyond the metal layer30 on at least two sides (e.g. at least ⅛ of an inch on two sides) inthe exemplary embodiment so that an adhesive regions 41 a and 41 b willextend slightly beyond the metal layer 30. The adhesive region 41 a willbond to the base member 28 and the adhesive region 41 b will slightlyoverlap, and bond to, a portion of the outer layer 40. The outer layer40 may, alternatively, cover the entire base member 28 (FIG. 6) or maycover the metal layer and some, but not all of the portion of the basemember proximal of the metal layer.

Another suitable manufacturing technique is the bladder mold process.Here, the fiber reinforced resin, metal, adhesive, outer layers areprearranged and then wrapped together around a bladder with a smallmandrel inside the bladder. A heated mold is placed over the wrappedbladder, the bladder is expanded to force the material against the mold,and the shaft is then cured in the mold. Curing times and temperaturesdepend on the polymer used in the composite and are well known to thoseof skill in the art. Filament winding techniques, where the process isstopped to change materials, may also be used. No adhesive is requiredhere because the graphite tow is wet with epoxy or other adhesive.

As noted above, the tip section 20 is substantially cylindrical, whilethe main body section 22 has a frusto-conical shape with a substantiallyconstant taper. In some embodiments, such as that illustrated in FIG. 6,it may be desirable to extend the metal layer 30 into the main bodysection 22. The inventor herein has determined that the discontinuity ofshape at the tip section/main body section junction 23 can, in someinstances, make rolling the metal layer 30 onto the base member 28difficult when the metal layer is formed from a single, continuous sheetof metal. One way to obviate this issue is to form the metal layer 30from two separate metal layer members. As illustrated for example inFIG. 7, a metal layer 30′ may be formed from a cylindrical metal layermember 44 and a frusto-conical metal layer member 46 that are arrangedas close to one another as practicable in the assembled shaft. The metallayer members 44 and 46 are formed from separate sheets of metal thatmay be rolled onto the base member 28 separately or simultaneously.

The rolling issue may also be obviated by forming a metal layer 30″ froma metal sheet (or “blank”) 48 having a plurality of longitudinallyextending slits 50 formed therein in the manner illustrated for examplein FIGS. 8 and 9. The length of the slits is 50 equal to the length ofthe portion of the metal layer within the main body section 22 (assumingthat the end of the metal layer 30″ opposite of the slits will bealigned with the tip end 26 of the shaft 12). When the metal sheet 48 iswrapped around the base member 28, the resulting metal layer 30″ willinclude a cylindrical metal layer member 52 and a series oflongitudinally extending metal layer members 54 that fan out from thecylindrical metal layer member to form the frusto-conical portion of themetal layer. The longitudinally extending slits 50 cause the formationof relief areas 56 between adjacent metal layer members 54, whichincrease in size as the distance from the cylindrical metal layer member52 increases.

Although the present inventions have been described in terms of thepreferred embodiment above, numerous modifications and/or additions tothe above-described preferred embodiments would be readily apparent toone skilled in the art. By way of example, but not limitation, thepresent inventions include golf clubs including any of the shaftsdescribed above. It is intended that the scope of the present inventionsextends to all such modifications and/or additions and that the scope ofthe present inventions is limited solely by the claims set forth below.

1. A golf club shaft for use with a golf club head including a hoselhaving a predetermined length, the golf club shaft comprising: a polymerbase member defining a tip end, a tip section adapted to be insertedinto the hosel, a main body section, a grip section, and a butt end; anda metal layer extending around and secured to at least a portion of thebase member tip section and defining distal and proximal ends, the metallayer being located such that the distal end of the metal layer is lessthan the predetermined length from the tip end and the proximal end ofthe metal layer is greater than the predetermined length from the tipend. 2-43. (canceled)